Amp Emulations

[jrc4558]

I love J-fet adaptations! They are very dynamic and way less compressed than whatever opamp/diode clippers I've heard. But I think I will lean towards the fact that they are not amplifier simulators. If anything, they are preamps + one mock poweramp/negative feedback stage.

[DDD]

Poor emulators shmemulators!
Shame on you guys :-)   Small stompboxes with the 8-Volt headroom vs 300 Volts and 50 pounds of copper, tungsten, steel and glass?
However, some of these tiny gadgets succesfully struggle against tube dictatorship.
At the same time, if we'll take at least 24 V power supply for FET/BJT/OpAmp simulation... did anybody try?

[WGTP]

Wow, this sure brought a lot of folks out.  Again demonstrating the overall coolness of this place.  

I really have to give this "movement" credit for helping me understand tube amps way better than I did, giving me the confidence to really look past the high voltage stuff and see what was going on.

To me this reinforces what R.G. and others have said for some time about the EQ being as important, if not more so, than the clipping mechanism.  Since many of the real amps are associated with different speaker systems, and the power output stages aren't being addressed, the EQ would seem to account for the largest part of the differences.

I remember 30 years ago being told that plugging a Fender head into a Marshall 1/2 stack made the 2 amps sound much more similar.

I guess we need to stick a Srypp/Mu/Blackfire/etc. stage at the end to cover the output stages.

As pointed out, there are many more similarities between the different versions than there are differneces.  I have wondered if a GENERIC 3-5 stage version couldn't be built with a few switches to account for the differences.

It is cool that you can plug Jfets into these circuits, designed for tubes and get a similar EQ effect.

Maybe we need to make up a word to describe these.  Anyone know any Latin?  Aron, you do the honors.

[petemoore]

  It isn't a 'coup' by Jfets to 'take over' anything...Emu...Simulator...whatever, if you see a 9v supply you can rest assured it's not a tube amp or tube preamp...[LV Tubes being the possible exception].
  So we know what we're looking at or can read it, and all about it, no hidden surprized.
  "Emu', IMO doesn't infringe on any existing names...nor can Jfets be confused with any four legged/hooved animals...it's just short for 'emulate'...ok Jfets don't emulate PS Sag and aren't exactly tubes..but do 'emulate' certain characteristics of a tube amp when 'carbon copied' into a Tube Preamp schematic '9v overlay'.
  "Emu' Seems to have stuck, as has countless other somewhat more innapropriate names...I like it cause it's short and is descriptive about what it 'does'.
  Read all about it or build 'em...and find out more for sure what's what W/ the Emu's..
  Not that there isn't a better nomenclature for these type devices....suggestions?

[markm]

ya know, I haven't built many of the EMU circuits but I have to say that the English Channel is a great sounding circuit for what it is. If I close my eyes it still sounds like a drive type pedal going through my Twin Reverb but, it sounds good none-the-less. I've learned a bunch from these circuits too.
This has been an interesting discussion to read.
Thanks fellas!!

[R.G.]

I guess it's time for me to say why I started this mess.

I'm very protective of beginners in the sense that if they ever get a wrong idea down as the truth, they then have to go UN-learn it before they can advance.

I think that a beginner seeing the term "JFET amp emulator" can easily get the idea that these are simple, straightforward recreations of the amps. We've seen examples of this view popping up in the forum frequently.

I don't think JFET triode replacement is a bad thing. Many of this kind of circuit sounds good on its own. But it will be reminiscent of the amp, not a re-creation of the amp. I think that the tone shaping over multiple stages is what is really giving the amp flavor, and that what does the distortion is less relevant.

I see the arguments about JFETs being simpler than an opamp distorter, but with the exception of the power pins, an opamp has the same number of pins as a JFET - three. Even taking into account the power pins, an opamp has either 4 pins per opamp (a dual) or 3.5 pins per opamp (quad). The circuits tend to take about the same number of resistors and caps. You'll need a diode or two extra to make the opamps distort, but it's much more predictable, especially than a JFET.

What the JFET replacements are is seemingly similar. There is an appeal to "well, just take out the triode and whip in a JFET in the same place, and it's the same". My interest in this is that the distortion/filtering/tone shaping get explored and understood, not just left at replacing triodes with JFETs

[petemoore]

  I like "Amp Sim"...
  Definition and pronunciation of 'Emulation'
  Effort or ambition to equal or surpass another.
Imitation of another.
  Jfet amp sims don't 'surpass' nor do they imitate particularly.
  And Simulation
  The act or process of simulating.
An imitation; a sham.
Assumption of a false appearance.
  *Imitation or representation, as of a potential situation or in experimental testing.
Representation of the operation or features of one process or system through the use of another:
  "Sham" is a bit Harsh, 'False appearance'..[if you haven't looked at the tube schematic...] *Imitation...
  I think by definition 'Sim' is closest to being appropriate...
  Kind of alludes to 'sim-ple'...Jfet Amp Sim's are certainly much simpler to do than a Tube Jfet Simulator.
  "Emu' is just fine by me, funny sounding word IMO...guides my thought train past the mammal every time...lol.
 

[R.G.]

Maybe "golem" applies 

[wordstep]

a little out of topic
I dont mind sb use 7 JFETto make a dirt box,
but use 9 opamps in serires  -- like Marshall (LXH2) sim two 9 opamps

I dont build one,but I believe it can sound good,but I do think it will completely kill the
dynamic - picking sensitivity, makebe good for recording - one way,but I dont think it is good for
practice - need dynamic,interactive.

anybody can tell me that I am completely wrong.

[R.G.]

I dont build one,but I believe it can sound good,but I do think it will completely kill the
dynamic - picking sensitivity, makebe good for recording - one way,but I dont think it is good for
practice - need dynamic,interactive.

anybody can tell me that I am completely wrong.

I think you are completely wrong.

Dynamic picking sensitivity can be had either way, and can be killed either way.

Of course, anyone can tell me I'm completely wrong.   

[tcobretti]

For a while my cousin used my ROG English Channel (Vox sim) as a preamp that he would run directly into the power amp of a Peavey 1x12 combo amp, and it sounded very good.  Whether or not it sounded much like a Vox is certainly questionable (I believe it is what we are discussing in this thread, right?), but it had a certain Voxiness, and certainly sounded much, much more tube like than the Peavey preamp it replaced.  So from my experience I have to say that it does not kill the sensitivity, and is in fact much more sensitive than most solid state amps.  My feeling about these pedals is that when properly tuned they manage to be better than most SS preamps, but not as good a real tube preamp.  I feel like many younger diyers who don't have nice amps could get A LOT of mileage from building a couple of these guys and using them as preamps.  Do they sound exactly like the amps upon which they are based? No, but they still sound very good.  My only real complaint is that to my ears (others here have disagreed with me before) they sound weird when driven with a dist/fuzz/booster.  But if you don't push the circuit too hard with a signal booster, they sound great.

I understand the problems with fet consistency, but if it were possible, a cheapo Marshall/Vox/Fender SS 1x12 using one of these would blow away the cheap crap they produce now. 

[aron]

At the same time, if we'll take at least 24 V power supply for FET/BJT/OpAmp simulation... did anybody try?

Of course. See the Shaka HV.

We've tried higher voltage, lower voltage, regulated voltage and lots of other things. Check the archives.

Op amp circuits can be very dynamic - and in a completely stable fashion.

So while we are talking "feel", I will venture to say that for the most part - that's my problem with most "digital" modelers. Except for hi-gain distortion, the feel is not right at all when played through hi-quality monitors etc...

It may "sound" alike, but not feel the same at all.

[wordstep]

wha,R.G. said I am completely wrong.I am think about change my ID and shutup 

I am kind of picky guy about picking dynamic,I use finger only,and play really light to a little heavy.
I do have a thought about how many onamps will kill picking dynamic.

lets say 7, put 7 onamp buffers in serires.....
of course,that is not fair, but just my thought.

I do respect, R.G. and a lot guys here. seriously.

[Gus]

Let me add some things

Lets think about this

look at the gain of the tube triode preamp stages then look at the operating points cathode voltage, plate voltage and plate current and B+

then look at the rp dynamic plate R

then check did you scale the output drive of the fet to the vol control EQ network

Then cal or measure the gain of the fet stage and then think about the 9V.  Your gain to output swing ratio could be different between a fet and tube circuit.  And you need to check the Vgd spec if you want to raise the voltage

then you need to think about input headroom

Here are some things to try

with opamp stages you can control each sections gain.  You can even offset the ref it does not have to be at 1/2. 
You might not want the output stage to be at 1/2 the 9V

If you look at the schematics on the web of trainwreck amps alot of the design seemed to be getting the Low pass and High pass and the stages gain just right.

Now if you read this far THINK BJTs

Simple BJT stages  can sound very good and you can control the gain, operation points Ic etc,( LPB, NPN and others)  You could design it so almost any Si small signal could drop in

Then download the duncan tone stack program and play.  First run some plots of tube amps you like so you know what you might want.

Check the solid state preamps in some marshalls like the 3005

Like R.G. posted it might be more the EQ.


If you look at the J201 specs they seem to be "tighter" than  some other fets IDSS .2ma to 1ma IIRC

FWIW I bought a bag of 1000 fairchild proccess 50 FETS and out of the hundreds I tested so far I have IDSS reading of 2ma to 15ma
I posted IDSS because it is a simple easy to do sort.

[Doug_H]

At the same time, if we'll take at least 24 V power supply for FET/BJT/OpAmp simulation... did anybody try?

Of course. See the Shaka HV.

We've tried higher voltage, lower voltage, regulated voltage and lots of other things. Check the archives.

Jack's Mini-tubes ran at 36v-40v IIRC. I think that's where we first got the idea to try higher voltages.

Op amp circuits can be very dynamic - and in a completely stable fashion.

Yes, the op amp circuit I mentioned earlier is much more touch-sensitive, finger-responsive, etc etc than any JFET circuits I've played with. It has nothing to do with the device type though.

The thing I could never get around with 9v pedal circuits is the fact that tube pre's are usually running around 200-250v for their supply voltage. Then there is a tradeoff between gain and clipping headroom that you can't duplicate at 9v- unless you attenuate the guitar signal down to scale it for the circuit. So a 100mv guitar signal @ 250v scales down to a 3.6mv signal @ 9v, if you have the same gain characterstic with the JFET that you would with a tube.

I could never figure out a way of doing that without overcomplicating it to a ridiculous point. In the end it's easier just to build a damn tube amp or - quit worrying about it, learn a few things from how amps are voiced and just concentrate on building some cool sounding pedals.

[John Lyons]

Well... It all comes down to what comes out of the speaker and into your ears. If you like what you hear then that's a "good" sound.

There is no point in comparing JFet bassed amp emulators to real tube amps but then there are a lot of amps that sound different even within the same model. Just because we all start with with the same schematic does not mean that we will end up the the same sound due to the amp, guitar speaker.... Then you go into amp choice, guitar, string, tube choice, speakers, guitar cables, picks, barometric pressure, phase of the moon,  etc etc etc.

There are a lot of variables. Everyone thinks differently and processes sound differently as well.

Even though a mesa Dual recitfier may sound different from the JFET Dr boogie, the DR boogie sounds really good (to my ears) and will get you at least 3/4 of the way there. Just the same as if you had a real DR and played it through a HIFI speaker. It's still a Boogie, it sounds a little different, but it's close enough...

John

[jrc4558]

Oh for crying out loud, SansAMP uses op-amps exclusively and one curent buffe BJT on the output! Does it has less dynamics that a FET based circuit? No no and no! But look up the schem and see how much frequency filtering/EQ goes on there!

[wordstep]

actually,I fround myself into some situation that I dont wanna into,
but on another hand,this is also a personal taste thing.

I like GDI21(GT2 clone) for a while,then after into some clean sound,I feel bad for it.
I really remember the day when someone ask how about base on 4049 chips pedal--dynamic or not.
I dont doubt why he ask,maybe I am wrong.

I can give one example is BOSS SD-2, one side 1 onamp,the other 5 in serires,
you know which one I hate and which one I like.

in a sentence,said JFET better than onamp---that is bull shit
actually I found my self dont like --say more than 5 onamp in serires.
of coures this is depend on shematics.

but in my poor knowledge,I assume there is at least 2 or more than 2 JFET in 1 onamp,and sometimes I can heard people say: the dual onamp chip has buffer inside
so buffer - bufer - buffer/onamp -onamp -onamp  .......

I think I made my point.
and I just assume that 5 JFET and 5 onamp(xx JFET inside) is a little different
------------------------------------------
and after I learn a few parallel design, maybe in - KLON/SPARKLE DRIVE/TONE PRESS
I found that a lot onamp in serires is not that popular,and suit my taste.

bite my taste if you can 

[puretube]

some early web-mentioning of FET/12AX7 similarity...

[MartyMart]

some early web-mentioning of FET/12AX7 similarity...

Jeez .... Tillman had the "Fenderish" Jfet preamp in '92  !!

Hmmmm.......